On 8/21/2017 2:08 PM, Alejandro Lucero wrote: > > > On Mon, Aug 21, 2017 at 11:34 AM, Ferruh Yigit <ferruh.yi...@intel.com > <mailto:ferruh.yi...@intel.com>> wrote: > > On 8/18/2017 5:23 PM, Alejandro Lucero wrote: > > > > > > On Fri, Aug 18, 2017 at 4:10 PM, Ferruh Yigit <ferruh.yi...@intel.com > <mailto:ferruh.yi...@intel.com> > > <mailto:ferruh.yi...@intel.com <mailto:ferruh.yi...@intel.com>>> wrote: > > > > On 8/11/2017 11:05 AM, Alejandro Lucero wrote: > > > A DPDK app could, whatever the reason, send packets with size 0. > > > The PMD is not sending those packets, which does make sense, > > > but the problem is the mbuf is not released either. That leads > > > to mbufs not being available, because the app trusts the > > > PMD will do it. > > > > > > Although this is a problem related to app wrong behaviour, we > > > should harden the PMD in this regard. Not sending a packet with > > > size 0 could be problematic, needing special handling inside the > > > PMD xmit function. It could be a burst of those packets, which can > > > be easily handled, but it could also be a single packet in a > burst, > > > what is harder to handle. > > > > > > It would be simpler to just send that kind of packets, which will > > > likely be dropped by the hw at some point. The main problem is how > > > the fw/hw handles the DMA, because a dma read to a hypothetical > 0x0 > > > address could trigger an IOMMU error. It turns out, it is safe to > > > send a descriptor with packet size 0 to the hardware: the DMA > never > > > happens, from the PCIe point of view. > > > > > > Signed-off-by: Alejandro Lucero <alejandro.luc...@netronome.com > <mailto:alejandro.luc...@netronome.com> > > <mailto:alejandro.luc...@netronome.com > <mailto:alejandro.luc...@netronome.com>>> > > > --- > > > drivers/net/nfp/nfp_net.c | 17 ++++++++++++----- > > > 1 file changed, 12 insertions(+), 5 deletions(-) > > > > > > diff --git a/drivers/net/nfp/nfp_net.c > b/drivers/net/nfp/nfp_net.c > > > index 92b03c4..679a91b 100644 > > > --- a/drivers/net/nfp/nfp_net.c > > > +++ b/drivers/net/nfp/nfp_net.c > > > @@ -2094,7 +2094,7 @@ uint32_t nfp_net_txq_full(struct > nfp_net_txq > > *txq) > > > */ > > > pkt_size = pkt->pkt_len; > > > > > > - while (pkt_size) { > > > + while (pkt) { > > > /* Copying TSO, VLAN and cksum info */ > > > *txds = txd; > > > > > > @@ -2126,17 +2126,24 @@ uint32_t nfp_net_txq_full(struct > > nfp_net_txq *txq) > > > txq->wr_p = 0; > > > > > > pkt_size -= dma_size; > > > - if (!pkt_size) { > > > + if (!pkt_size) > > > /* End of packet */ > > > txds->offset_eop |= > PCIE_DESC_TX_EOP; > > > - } else { > > > + else > > > txds->offset_eop &= > > PCIE_DESC_TX_OFFSET_MASK; > > > - pkt = pkt->next; > > > - } > > > + > > > + pkt = pkt->next; > > > /* Referencing next free TX descriptor */ > > > txds = &txq->txds[txq->wr_p]; > > > lmbuf = &txq->txbufs[txq->wr_p].mbuf; > > > issued_descs++; > > > + > > > + /* Double-checking if we have to use > chained > > mbuf. > > > + * It seems there are some apps which > could > > wrongly > > > + * have zeroed mbufs chained leading > to send > > null > > > + * descriptors to the hw. */ > > > + if (!pkt_size) > > > + break; > > > > For the case chained mbufs with all are zero size [1], won't > this cause > > next mbufs not freed because rte_pktmbuf_free_seg(*lmbuf) used? > > > > > > Good point. Being honest, we had the problem with mbufs and size > 0, and > > this last check > > was not initially there. But we saw performance being low after the > > change, and the only thing > > which could explain it was this sort of chained mbufs. There was not > > mbuf allocation problem at > > all. It was like more (null) packets being sent to the hardware now. > > This last check solved the > > performance problem. > > I assume performance problem is with the chained mbufs with 0 size, I > believe this should be fixed in application, not in PMD level. > > And if application is sending chained mbufs with 0 size, with above code > it will eventually be out off mbufs, since they are not freed, and same > problem will occur that this patch is trying to avoid, but perhaps in > longer run. > > > This is definitely an app problem and maybe that last check should be > avoided and to process that chained mbuf, whatever is it coming from, if > "pkt = pkt->next" is not null. > > Are you OK of I send another version without that last if clause?
Yes, thank you. > > > > > > > Once I have said that, I have to admit my explanation implies some > > serious problem when > > handling mbufs, and something the app is doing really badly, so I > could > > understand someone > > saying this is hidden a serious problem and should not be there. > > > > [1] > > As you mentioned in the commit log, this not correct thing to > do, but > > since patch is trying to harden PMD for this wrong application > > behavior.. > > > > > > If you consider this last check should not be there, I'll be glad to > > remove it. > > > > > > > > > } > > > i++; > > > } > > > > > > > > >
